U.S. refiner Tesoro Corp has received formal approval from California's attorney general to buy a BP Plc refinery for more than $2 billion.

Attorney General Kamala Harris said her office and the California Energy Commission would monitor gas prices, volume and refinery capacity. A deal with the company also provides for safeguards against price spikes.

The U.S. Federal Trade Commission, which assessed the deal to ensure it complies with antitrust law, also approved the proposed transaction on Friday.

(Reporting by Diane Bartz; Editing by Richard Chang)